IMPORTANT MINERALS IN AGRICULTURE:

ESSENTIAL AND CONTAMINANTS

National Science and Technology Forum (NSTF) 19 March 2019

Harry Dube

Technical Advisor

Department of Agriculture, Forestry and Fisheries

Directorate: Agriculture Inputs Control

Agriculture Inputs Control (Act 36 of 1947)

Act 36 of 1947

Fertilizers

Farm Feeds

Agricultural Remedies

Stock Remedies

Pest Control operators

Sterilizing Plants

2

The Current Regulatory Model

3

•Registrar assesses submitted documents for efficacy and safety

•Product label must contain prescribed information

Company or Individual apply

to register product

•Facility must be suitable for intended purpose

•Facility must comply with relevant regulations

Registrar Inspects

manufacturing facility

•Advertisements of product must be approved by Registrar •Registration holder expected to monitor product safety and report any safety concerns to Registrar

Product registered for

retail

Locally manufactured products

• Inspectors verify that manufacturing facility complies with prescribed South African regulations

• Product must be suitable and sufficiently effective for the purpose for which it is intended and comply with prescribed South African regulations

Imported

• Prove that manufacturer complies with legislation in country of origin

• Prove that manufacturer has a quality management system in place

• Product must be suitable and sufficiently effective for the purpose for which it is intended and comply with prescribed South African regulations

• Registration of products manufactured or imported for retail

• Locally manufactured products by farmers for own use do not require registration

The Current Regulatory Model

• Work in conjunction with Department of Health (MRLs)

• Environmental affairs (NEMA, NEMBA)

• SAPS (Explosives Act)

• Consideration of international protocols that South Africa ratified

• Stockholm Convention (on POPs)

• Rotterdam conventions (on hazardous chemicals and pesticides)

• Basel convention (movement of hazardous waste and disposal)

• Montreal protocol (on substances that depletes the Ozone)

4

Background (Act 36 of 1947)

• support innovation, expedite time to market for safe and quality, pesticides,

animal medicine, fertilizer and animal feeds in agricultural production, to

further the well-being of South Africa’s people, environment, and economy.

• We achieve this by making sure that agricultural inputs in the country are

registered and have a unique registration number

• The registration process ensures that any product used in the agricultural

sector is fit for purpose, effective and safe for use by humans, animals and

that it does not cause harm to the environment.

5

Background (Act 36 of 1947)

• Fertilizer means any substance which is intended or offered to be used

for improving or maintaining the growth of plants or the productivity of

the soil

• It includes natural or synthetic product applied to plant tissue or directly

to soil to benefit plants direct or indirectly.

• Includes inorganic fertilizers, organic fertilizers, plant growth

regulators, copolymers, urease inhibitors, plant extracts, sea weed

products, amino acids, chelating and complexing agents.

6

Essential Plant Nutrients

• Structural Plant nutrients: Obtained from water and the atmosphere

(Hydrogen, Carbon & Oxygen)

• Macro nutrients : Three primary and Three secondary (Nitrogen, Phosphorus

Potassium & Calcium, Magnesium, Sulphur)

• Micronutrients: chlorine, boron, manganese, iron, copper, Zinc,

Molybdenum cobalt, nickel.

• Good and productive soils maintain a healthy balance of these nutrients

together with soil biota and organic matter.

7

Sources of Plant Mineral Nutrients

Nutrient Source

Nitrogen Haber/Bosch process

Potassium Mining (Potash, Orthoclase feldspar)

Phosphorus Mining (Rock phosphate)

Calcium Mining (Lime) (CaCO3)

Magnesium Mining (Dolomitic Lime)

Sulphur Cleaning of fossil fuel(Removal of S)

Zinc Mining

Boron Mining (Colemanite, tincal, kernite)

Molybdenum Mining (Molybdenite)(sodium molybdate)

Manganese Mining

Copper Mining

Iron Mining 8

Effect of pH nutrient availability

9

Micro nutrient concentrations in soils

10

Essential plant nutrients

• Most agricultural soils rarely have a well balanced plant nutrients

• Or nutrients are in unavailable forms (eg Phosphorus)

• This result in heavy losses in crop yield and financials

• Fertilizers are usually used to correct any soil deficiencies

11

Some of deficiencies manifest in plant symptoms

12

Phosphorus deficiency in Maize

13

Boron Deficiency in Papaya

14

Iron deficiency in macadamia

15

Molybdenum deficiency in onion

16

Manganese deficiency in orange

17

Phytotoxic mineral elements

Some minerals, although required in small quantities. They are:

• Boron

• Manganese

• Chlorine

• Zinc

• Iron

• Copper

Their availability is influenced by different factor including soil pH, temperature, humidity

and management

18

Minerals of concern

• Some minerals found in soils are toxic to humans, soil biota, marine animals and plants.

Unfortunately most occur in natural environments and their background concentrations

are naturally above recommended concentrations by Department of Environmental

Affairs and Environmental Protection Agencies.

• Most regulators have maximum permissible limits in fertilisers (Absolute values)

• They are:

• Cadmium

• Arsenic

• Mercury

• Cobalt

• Selenium

• Chromium

• Nickel

• Molybdenum

19

Heavy Metal limits in fertilizers

20

Cadmium (Cd)

• One of the most Eco toxic minerals in soils

• Concern is that toxicity in plants may not be visible in plants yet very toxic to mammals

• Cadmium is more mobile in neutral soil conditions

• It mostly occurs mostly with phosphorus deposits (rock phosphate)

• Due to anthropogenic processes Cd concentrations can be high sewage sludge and

municipal solid waste compost

• Symptoms of Cd poisoning in plants include stunting, leaf roll and chlorosis.

• Threat: In 2007 a consignment pineapples was returned due to Cd contamination as a

result of usage of high Cd unregistered fertilizers.

21

Arsenic

• Non essential metalloid to plants and animals

• Classified as carcinogenic by International Agency of Research on Cancer (IARC)

• Known to accumulate in edible plant parts after crop uptake

• Occurs in the environment either as Arsenate (V) and Arsenite (III) with the latter being

more toxic

• Inhibit plant growth resulting in decreased crop yield

• Plants that evolved in high As backgrounds are more tolerable to high As concentration.

• Tobacco known to be a hyperacumulator of As

22

Chromium (Cr)

• Two stable form of Cr occur in nature depending oxidative state: Cr(VI) and Cr (III)

• Cr (VI) is the most toxic form

• Other than occupational exposure people get exposed to Cr through the food chain in

vegetables and Fruits

• Generally Cr is retained in plant roots and not easily translocated to shoots.

23

Mercury (Hg)

• One of the non essential minerals that occur naturally in soils due to natural rock

formations

• Can induce seed injury and limits crop yields

• Hg is generally not easily translocated to plant shoots

• Toxic to soil biota, fish and terrestrial animals

24

Toxic (Cu, Fe, Se, Ni, Mo)

• These are essential elements that are required by plants but in greater quantities they

become toxic to plants

• When they enter the food chain through crop production they can become toxic to

humans and animals

• Selenium is a very important nutrient in alfalfa but can be very toxic to other plants and

humans.

• Nickel deficiency is of big concern in pecan nuts but poor management can result in

contaminated soils not suitable other crops

• Cu, Fe and Mo are essential micronutrients but can end up in the food chain due to

exessive usage as a fertilizer or pesticides

• The need to protect South African consumers from contaminated produce as much as

exported products are.

25

New Developments in the agricultural sector

• The use of K , Na poly acrylates as water retentioners gaining traction

• Use of controlled released fertilisers to increase soil residency time and reduced

leaching and vaporisation

• Polymer coated nitrogen products

• Nutrient recycling

• Usage of complexing and chelating metals (Fe, Cu, Mn) for better crop uptake and soil

adsorption.

• Banning of undesirable products as soon as they are listed in the Stockholm (POPs)

and other conventions that South Africa is a signatory

• Recognition of nickel and silicon as essential elements

26

Conclusion

• Fertilizers form a very important part of food production, food security.

• Crop production activities mine important minerals out of the soil which result in a need

for the use of fertilizers.

• Mineral resource in South Africa ( and the world) are finite-require better management.

• The need to protect the environment from unintended consequences of fertilizer

application

• The use of fertilizers comes with is a risk of heavy metal accumulation in soils

• A need to better regulate nitrogen fertilizers to avoid leaching and volatilisations

• Organic Fertilizers tend to be hit or miss if poorly processed otherwise the cost

escalates.

27

THANK YOU

28